Maybe so, Collin. I remember about 10 years ago people thinking that email would soon die because of spam overtaking all email systems and defeating emails functionality. Well, still hasn't happened.
Apple computer, with all of its security features on the iPhone, was unable to stop the government from breaking in. Hilary Clinton was unable to prevent her personal server from being broken into (I believe that she had some of the best IT folks working for her.) So when will computers be totally secure? Probably never.
Getting back to Moodle... Don't use self-registration. Yep, manually enter all of your users, or import them.